Interleukin-6 (IL-6) is a well known cytokine whose biological activitities are mediated by a membranal receptor system comprising two different proteins one named IL-6 Receptor (IL-6R or gp80) and the other gp130 (reviewed by Hirano et al, 1994). Soluble forms of IL-6R (sIL-6R), corresponding to the extracellular domain of gp80, are natural products of the human body found as glycoproteins in blood and in urine (Novick et al, 1990, 1992). An exceptional property of sIL-6R molecules is that they act as potent agonists of IL-6 on many cell types including human cells (Taga et al, 1989; Novick et al, 1992). This is due to the fact that even without the intracytoplasmic domain of gp80, sIL-6R is still capable of triggering the dimerization of gp130 in response to IL-6, which in turn mediates the subsequent IL-6-specific signal transduction and biological effects (Murakami et al, 1993). The active IL-6 receptor complex is in fact a hexameric structure formed by two gp130 chains, two IL-6R and two IL-6 ligands (Ward et al, 1994; Paonessa et al, 1995), in which sIL-6R has two types of interaction with gp130 both of which are essential for the IL-6-specific biological activities (Halimi et al, 1995).
Treatment with sIL-6R results in an enhancement of the biological activities of IL-6 in many cell types. An example is tumor cells whose growth is inhibited to a greater extent by IL-6 when sIL-6R is added, such as murine myeloleukemic M1cells (Taga et al, 1989), human breast carcinoma T47D cells (Novick et al, 1992) or human Non-small cell lung carcinoma cells (Ganapathi et al, 1996). IL-6 has anti-metastatic activities in vivo (Katz et al, 1995), sIL-6R and can also enhance such in vivo anti-tumor effects of IL-6 (Mackiewicz et al 1995). Another activity of IL-6 which is enhanced by sIL-6R addition, is the stimulation of hematopoietic stem cells to produce multilineage colonies (Sui et al, 1995). The present inventors have also observed that the survival of primary cultures of brain oligodendrocytes is supported by the sIL-6R and IL-6 combination (Oh, 1997), while IL-6 alone is poorly active in such cultures (Kahn and De Vellis, 1994). This finding indicates that IL-6, when combined with sIL-6R, can mimic the activity of other neurotropic cytokines such as Ciliary Neurotropic Factor (CNTF) or Leukemia Inhibitory Factor (LIF) which also act through gp130, as is also the case for IL-11 and Oncostatin M (Hirano et al, 1994).
In an attempt to provide a molecule which may combine the above noted functions of IL-6 and sIL-6R, there has recently been reported the production in recombinant yeast cells of a fusion protein between a truncated segment of the human IL-6R sequence and IL-6, linked by a glycine-rich linker (Fischer et al., 1997). This fusion protein includes essentially only the IL-6R cytokine receptor N-domain and the cytokine receptor C-domain, and thus lacks essentially all of the IL-6R immunoglobulin (Ig)-like domain, and the receptor pre-membrane region (the region between the C-domain and the transmembranal domain). As such it represents a truncated form of the sIL-6R, this truncated sIL-6R in the fusion protein being linked via the above noted glycine-rich linker to essentially the whole mature form of IL-6. Besides lacking parts of the natural sIL-6R, this fusion protein by being produced in yeast cells, does not have the glycosylation pattern that such a fusion protein would have if it were produced in mammalian cells, in particular, e.g. in human cells. In fact, this yeast-produced fusion protein has a molecular weight of only about 57 kDa in contrast to a fusion product containing essentially all of the natural sIL-6R and IL-6 amino acid residues and being fully glycosylated in mammalian (e.g. human) cells, which has the expected molecular weight of about 85 kDa (see Example 2 herein below).
The common experience in developing recombinant proteins which can be used for treating human patients has shown that it is important to remain as close as possible to the natural forms of the proteins, as they are found in the human body, in order to avoid triggering of antibodies and other side effects observed with non-natural recombinant products. For this reason, it has been advantageous to use recombinant mammalian cell systems to produce glycosylated proteins such as Interferon-βor Granulocyte-colony stimulating factor (Chernajovsky et al, 1984, Holloway, 1994) in a chemical form as similar as possible to the natural human product. Bacteria or microorganisms such as, for example, yeasts, which do not glycosylate properly, also cause the wrong folding of the protein chains, leading to immunogenic reactions. This is particularly important in respect of IL-6 which is heavily modified postranslationally by N- and O- glycosylation as well as by phosphorylation (Revel, 1989 for review), and in respect of the natural sIL-6R from human blood and urine which is a glycoprotein whose N-terminus and C-terminal amino-acids are constant and have been determined (Novick et al, 1990 and co-owned patents by the present inventors Nos. U.S. Pat. No. 5,216,128 and its corresponding EP 413908 B1).
Accordingly, it would seem that the above noted previous fusion product between part of the sIL-6R and IL-6 has a number of possible drawbacks especially as regards its use for treating humans and this, due to the fact that it lacks part of the sIL-6R, as well as its production in yeasts which may provide for incorrect glycosylation of the protein.
Heretofore, a fusion molecule comprising the natural sIL-6R found in human body fluids and the natural IL-6, and which is produced in human or other mammalian cells, has not been described.
It is therefore an aim of the present invention to provide such a fusion molecule comprising the natural sIL-6R and the natural IL-6 (in any order) which is produced in mammalian cells.
It is another aim of the present invention to use such a fusion protein (sIL-6R/IL-6 chimera) to inhibit the growth of highly metastatic melanoma cells at very low concentrations, these cells being resistant to IL-6 or sIL-6R alone.
Yet another aim is to use such a fusion protein (the sIL-6R/IL-6 chimera) for the in vivo engraftment of human hematopoietic stem cells in bone marrow transplantation protocols.
It is a yet further aim of the present invention to use such a fusion protein in other IL-6 related disorders, e.g. liver conditions or neurological conditions.
A further aim of the invention is to provide pharmaceutical compositions which contain the above mentioned natural sIL-6R-natural IL-6 fusion protein (sIL-6R/IL-6 chimera) for the treatment of cancer, for use in bone marrow transplantation procedures, and for other IL-6 related disorders, e.g. liver conditions and neurological conditions.
Other aims and aspects of the present invention will be set forth or will arise from the following disclosure of the present invention.